I think that it is not correct to see the Balrog in a western middle-age christian or jewish conception. Being an Italian, i know very well Dante's Inferno and the numerous church's depiction, and nothing is so far from the Tolkien's Balrog. We must think to this creature in a classic hellenic conception as fire "spirit" or Essence bearer, that is a good being if not corrupted by Morgoth: this is probably the true idea of Tolkien. Maybe an huge manlike being without horns, wings or tail and NOT a piglike or troll-like face. It is probable that he has a very beautifull look, when not burning.